UPDATE December 2020 - The Environment Agency have updated the database. The easiest way I have found after lots of searching to view the results is to follow this link
And turn of the EXTENTS map layer.
UPDATE 2018 - since I wrote this post techniques have moved on:
1) Got to https://www.lidarfinder.com/ - fantastic, job done.
2 Or https://houseprices.io/lab/lidar/map does it all for you
Ever since the Environment made their LIDAR data for most of England free to use I have been meaning to find a simple way to view it that didn't involve map geekery.
So here is my simple guide so I remember how to do it again, and it might interest you as well.
1) Go to https://data.gov.uk/publisher/environment-agency
2) Click on LIDAR Composite DTM - 2m or one of the other LIDAR data sets (doesn't matter much which at this point).
3) Click on blue "Preview on Map" button
You will then have a map of the UK and a long list of possible active layers on the left.
Scroll down and choose the LIDAR layer you want and zoom in on the map to the area you want.
Not all of England is covered and there are different levels of detail - and it is available as a Digital Surface Model produced from the signal returned to the LIDAR (which includes heights of objects, such as vehicles, buildings and vegetation, as well as the terrain surface) or as a Digital Terrain Model produced by removing objects from the Digital Surface Model.
Click to embiggen
https://houseprices.io/lab/lidar/map does it all for you -
Here as an example is Bladon Camp - heavily overgrown so aerial Bing Map shot doesn't really show it but LIDAR does - https://historicengland.org.uk/listing/the-list/list-entry/1013234 for details of it.
A commentator, Sem, on http://www.megalithic.co.uk/modules.php?op=modload&name=Forum&file=viewtopic&topic=6761&forum=2&start=0 points out that there is some Welsh data available as well.
http://lle.gov.wales/home?lang=enAnd here is a screen shot from Anglesey with a well known barrow in it :)
To use on-line click on 'LiDAR Data Now Available' followed by the link to 'lle download portal" and finally on 'Preview'. Navigate the map as per Google and use the 'blue thingy' in the top right of the map to choose your base map and detail.